In this renewal application of our NIA grant concerning the synthesis and pharmacological characterization of agents for the treatment of memory and learning disorders, it is our aim to continue work on he development of huperzine A and its analogues as palliative agents for the treatment of Alzheimer's dementia (AD) and other age-related memory impairments. In view of the intriguing pharmacological profile exhibited by huperzine A, our own preliminary behavioral experiments, as well as the behavioral and clinical experiments conducted in China, we believe that more extensive structure-activity relation (SAR) studies need be conducted. We are optimistic that a useful, more effective, and less toxic acetylcholinesterase (AChE) inhibitor than those currently available can be identified for clinical use. While we are cognizant of the fact that defects in neurotransmitter systems other than the cholinergic system play a role in the memory loss associated with AD, findings by Davis and others indicate that ACHE inhibitors (e.g., physostigmine) do show modest cognitive improvement, and may prove useful in combination with other drugs (e.g., clonidine, deprenyl, or desipramine). Specifically, the use of an AChE inhibitor in combination with an efficacious M2 antagonist (a facilitator of ACh release) may constitute an attractive therapeutic strategy. Accordingly, we intend to expand Our program in the huperzine area to encompass the following objectives: (1) Investigate further improvements in the established synthesis of (-)-huperzine A in order to facilitate its scale-up; (2) Prepare a number of additional, carefully selected analogues of huperzine A which embody both steric and electronic alterations; (3) Determine the IC50 Of all new analogues for the inhibition of acetylcholinesterase in vitro, and use this information to refine electrostatic and steric coefficient contour maps predictive of activity through use of the Tripos comparative molecular field analysis (COMFA) program; (4) For compounds found to be potent in the in vitro ACHE assay, carry out muscarinic and nicotinic binding experiments in addition to BuChE (butyrylcholinesterase) assays in order to establish the selectivity of action and absence of receptor blocking effects; (5) Subsequently test the most promising ACHE inhibitors for their effect on ACh and choline levels and ACHE activity in vivo; (6) To ascertain penetration of the blood-brain-barrier, determine the CNS/PNS ratio for selected analogues of therapeutic value; (7) To determine distribution and possible metabolism in brain, radiolabel the most promising compounds and assay radioactivity of metabolites in extracts.